52 PROCEEDINGS OF THE AMERICAN ACADEMY 



regions (as partially shown in Hooker's Flora Boreali- Americana), but 

 also in the more southern parts. 



And, in fact, my inquiries have persuaded me that the similarity or 

 analogy in this respect is greater than is generally supposed. With 

 my experience of the European Willows, which frequently vary from 

 one extremity of size, form, and color to another, according to the area 

 of the species (e. g. S. nigricans), and which in different countries not 

 seldom have the most diflerent aspects (e. g. S. Lapponum and aS'. glauca 

 in Lapland and Switzerland), I could not be surprised to find many 

 American Willows equally varying from ours, although certainly be- 

 longing to European types, or at least so analogous to their European 

 relatives that they might be considered as subspecies of them, till we 

 discover the intermediate forms which are the connecting links of that 

 unbroken series which we may consider as constituting a true natural 

 genus. This idea, is it anything more than my individual opinion ? 

 It must be proved by others ; it must be ascertained by diligent, un- 

 prejudiced, and accurate researches upon the living species in America, 

 and especially by botanists who have acquired a pi'ofound acquaintance 

 with the European species, as older in the history of the science. 



My esteemed correspondent, Professor Asa Gray, who has kindly 

 promised to assist me in procuring materials for a more complete trea- 

 tise upon this very difficult genus, has encouraged me to send him an 

 enumeration of the American species already known to me, which may 

 be brought to the notice of botanists of the United States generally, in 

 the hope that they may be induced to make renewed and cx'itical obser- 

 vations upon the species indigenous ax-ound them, and also to favor me 

 with contributions of specimens, which are so greatly needed to perfect 

 my contemplated revision of the entire genus for De CandoUe's Pro- 

 dronms. 



I have tried to lay before the reader some of the reasons why I must 

 consider several American species as very much allied to, or perhaps 

 identical with, ours in the Old World. But neither time at present, 

 nor the space at my command, has permitted me to treat the matter at 

 the length requisite to prove the correctness of my opinion. I have 

 also been obliged to restrict this communication to short diagnoses only 

 for the new species here proposed, and to a few synonymes from the 

 principal American Floras. Should this essay fulfil its purpose of 

 directing the attention of the botanists of the United States to this diffi- 



